Rapid determination of molecular parameters of synthetic polymers by precipitation/redissolution high-performance liquid chromatography using ?molded? monolithic column

Novel biologically active polyurea derivatives and its TiO2-doped nanocomposites

A new series of polyurea derivatives and its nanocomposites were synthesised by the solution polycondensation method through the interaction between 4(2-aminothiazol-4-ylbenzylidene)-4-(tert-butyl) cyclohexanone and diisocyanate compound in pyridine. The PU1-3 structure was confirmed using Fourier transform-infrared (FTIR) spectroscopy and characterised by solubility, viscometry, gel permeation chromatography (GPC), and X-ray diffraction (XRD) analysis. In addition, PU1-3 was evaluated by TGA. Polyurea-TiO2nanocomposites were synthesised using the same technique as that of PU1-3 by adding TiO2 as a nanofiller. The thermal properties of PU2TiO2a-d were evaluated by TGA. Moreover, the morphological properties of a selected sample were examined by SEM and TEM. In addition, PU1-3 and PU2TiO2a-d were examined for antimicrobial activity against certain bacteria and fungi. The PU1-3 showed antibacterial activity against some of the tested bacteria and fungi, as did PU2TiO2a-d, which increased with the increase in TiO2 content. Furthermore, molecular docking studies were displayed against all PU1-3 derivatives against two types of proteins. The results show that the increase in the strength of π-H interactions and H-donors contributed to improved binding of PU2 compared to PU1 andPU3. The docking of 1KZN against the tested polymers suggests an increase in the docking score of PU2, then PU1, and PU3, which is in agreement with the antibacterial study.

Macroporous Gel with a Permeable Reaction Platform for Catalytic Flow Synthesis

We mimic a living system wherein target molecules permeate through capillary and cells for chemical transformation. A monolithic porous gel (MPG) was easily prepared by copolymerization of gel matrix, tertiary amine, and cross-linking monomer in one-step synthesis. Interconnected capillaries existed in the MPG, enabling flow application with high permeability. Because the capillaries were constituted of polymer gel, Pd(0)-loaded MPG provided another permeable pathway to substrates in a gel network, contributing to its much high turnover number after 30 days of use, compared with that of Pd(0)-loaded inorganic supports. Interestingly, the gel network size of the MPG influenced the catalytic frequency. Diffusivities of the substrates and product in the gel networks increased with increasing network sizes in relation to catalytic activities. The MPG strategy provides a universal reactor design in conjunction with a practical process and precisely controlled reaction platform.

Glycopolymer monoliths for affinity bioseparation of proteins in a continuous-flow system: glycomonoliths

Macroporous materials, called glycomonoliths, were prepared from saccharide-containing monomers, and applied for affinity bioseparation of proteins in a continuous-flow system.

Cross-linker effects on the separation efficiency on (poly)methacrylate capillary monolithic columns. Part I. Reversed-phase liquid chromatography

We synthesized 8 polymethacrylate monolithic capillary columns using laurylmethacrylate functional monomer and various cross-linking monomers differing in the polarity and size. The efficiency of monolithic columns for low-molecular compounds significantly improved with increasing number of repeat non-polar methylene groups in the cross-linker molecules, correlating with greater proportion of small pores with size less than 50 nm. The best efficiency with HETP=25 μm for alkylbenzenes was achieved for columns prepared using hexamethylene dimethacrylate (HEDMA). Columns prepared with polar (poly)oxyethylene dimethacrylate cross-linkers show also improved efficiency with increasing chain length and generally better performance in comparison to the (poly)methylene dimethacrylate cross-linkers of comparable size, however with less apparent effects of the chain lengths on the pore distribution. The monolithic columns prepared with tetraoxyethylene dimethacrylate (TeEDMA) showed the best efficiency of all the columns tested, corresponding to HETP=15 μm (approx. 70,000 theoretical plates/m), show excellent column-to-column reproducibility with standard deviations of 2.5% in retention times, good permeability and low mass transfer resistance, so that is suitable for fast separation of low-molecular compounds in 2 min or less. By modification of the fused-silica capillary inner walls pre-treatment procedure, very good long-term stability was achieved even in 0.5 mm i.d. capillary format. The TeEDMA column can be also used for size-exclusion chromatography of lower non-polar synthetic polymers, whereas it is less suitable for separations of proteins than the HEDMA column.

Recent advances in the design of organic polymer monoliths for reversed-phase and hydrophilic interaction chromatography separations of small molecules

Owing to their favorable porous structure with pore size distribution shifted towards large flow-through pores, organic polymer monoliths have been mainly employed for the separation of macromolecules in gradient elution liquid chromatography. The absence of significant amounts of small pores with a stagnant mobile phase and the resulting low surface area were considered as the main reason for their poor behavior in the isocratic separation of small molecules. Several recent efforts have improved the separation power of organic polymer monoliths for small molecules offering column efficiency up to tens of thousands of plates per meter. These attempts include optimization of the composition of polymerization mixture, including the variation of functional monomer, the cross-linking monomer, and the porogen solvents mixture, adjustment of polymerization temperature, and time. Additionally, post-polymerization modifications including hypercross-linking and the use of carbon nanostructures showed significant improvement in the column properties. This review describes recent developments in the preparation of organic polymer monoliths suitable for the separation of small molecules in the isocratic mode as well as the main factors affecting the column efficiency.

Stability and repeatability of capillary columns based on porous monoliths of poly(butyl methacrylate-co-ethylene dimethacrylate)

Monolithic poly(butyl methacrylate-co-ethylene dimethacrylate) capillary columns have been prepared via either thermally or photochemically initiated polymerization of the corresponding monomers and the repeatability of their preparation has been explored. Three separate batches of 5 columns each were prepared using thermal and photochemical initiation for a total of 30 columns. All 30 capillary columns were tested in liquid chromatography-electrospray ionisation mass spectrometry mode for the separation of a model mixture of three proteins--ribonuclease A, cytochrome c and myoglobin. Excellent repeatability of retention times was observed for the proteins as evidenced by relative standard deviation (RSD) values of less than 1.5%. Somewhat broader variations with RSD values of up to 10% were observed for the pressure drop in the columns. The stability of retention times was also monitored using a single monolithic column and no significant shifts in either retention times or back pressure was observed in a series of almost 2200 consecutive protein separations.

Preparation and HPLC applications of rigid macroporous organic polymer monoliths

Rigid porous polymer monoliths are a new class of materials that emerged in the early 1990s. These monolithic materials are typically prepared using a simple molding process carried out within the confines of a closed mold. For example, polymerization of a mixture comprising monomers, free-radical initiator, and porogenic solvent affords macroporous materials with large through-pores that enable applications in a rapid flow-through mode. The versatility of the preparation technique is demonstrated by its use with hydrophobic, hydrophilic, ionizable, and zwitterionic monomers. Several system variables can be used to control the porous properties of the monolith over a broad range and to mediate the hydrodynamic properties of the monolithic devices. A variety of methods such as direct copolymerization of functional monomers, chemical modification of reactive groups, and grafting of pore surface with selected polymer chains is available for the control of surface chemistry. Since all the mobile phase must flow through the monolith, the convection considerably accelerates mass transport within the molded material, and the monolithic devices perform well, even at very high flow rates. The applications of polymeric monolithic materials are demonstrated mostly on the separations in the HPLC mode, although CEC, gas chromatography, enzyme immobilization, molecular recognition, advanced detection systems, and microfluidic devices are also mentioned.

Porous polymer monoliths: an alternative to classical beads

Porous polymer monoliths are a new category of materials developed during the last decade. These materials are prepared using a simple molding process carried out within the confines of a closed mold. Polymerization of a mixture that typically contains monomers, free-radical initiator, and porogenic solvent affords macroporous materials with large through-pores that enable flow-through applications. The versatility of the preparation technique is demonstrated by its use with hydrophobic, hydrophilic, ionizable, and zwitterionic monomers. The porous properties of the monolith can be controlled over a broad range. These, in turn, determine the hydrodynamic properties of the devices that contain the molded media. Since all the mobile phase must flow through the monolith, the mass transport within the molded material is dominated very much by convection, and the monolithic devices perform well even at very high flow rates. The applications of monolithic materials are demonstrated on the chromatographic separation of biological compounds and synthetic polymers, electrochromatography, gas chromatography, enzyme immobilization, molecular recognition, and in advanced detection systems. Grafting of the pore walls with selected polymers leads to materials with completely changed surface chemistries.

Monolithic stationary phases for liquid chromatography and capillary electrochromatography

A monolithic stationary phase is the continuous unitary porous structure prepared by in situ polymerization or consolidation inside the column tubing and, if necessary, the surface is functionalized to convert it into a sorbent with the desired chromatographic binding properties [J. Chromatogr. A 855 (1999) 273]. Monolithic stationary phases have attracted considerable attention in liquid chromatography and capillary electrochromatography in recent years due to their simple preparation procedure, unique properties and excellent performance, especially for separation of biopolymers. This review summarizes the preparation, characterization and applications of the monolithic stationary phases. In addition, the disadvantages and limitations of the monolithic stationary phases are also briefly discussed.

Porous polymer monoliths: simple and efficient mixers prepared by direct polymerization in the channels of microfluidic chips

Porous monolithic polymers have been prepared by photoinitiated polymerization of mixtures consisting of 2-hydroxyethyl methacrylate, ethylene dimethacrylate, UV-sensitive free radical initiator and porogenic solvent within channels of specifically designed microfluidic chips and used as micromixers. Substituting azobisisobutyronitrile with 2,2-dimethoxy-2-phenylacetophenone considerably accelerated the kinetics of the polymerization. Mixtures of cyclohexanol and 1 -dodecanol and of hexane and methanol were used, respectively, to control the porous properties and therefore the mixing efficiency of the device. The performance of the monolithic mixers has been tested by pumping aqueous solutions of two fluorescent dyes at various flow rates and monitoring the point at which the boundary of both streams completely disappears. Best results were achieved with a monolithic mixer containing very large irregular pores.